1. Technical Field
The present invention relates generally to the manufacturing of semiconductor devices, and in particular to chemical mechanical polishing of substrates. Still more particularly, the present invention relates to a method and apparatus for actively adjusting conditions used in chemical mechanical polishing of a substrate to improve polishing uniformity of the substrate.
2. Description of the Related Art
In certain technologies, such as integrated circuit fabrication, optical device manufacture and the like, it is often crucial to the fabrication processes involved that the workpiece from which the integrated circuit, optical, or other device is to be formed have a substantially planar front surface and, for certain applications, have both a planar front surface and back surface.
One process for providing such a planar surface is to scour the surface of the substrate with a conformable polishing pad, commonly referred to as "mechanical polishing". When a chemical slurry is used in conjunction with the pad, the combination of slurry and pad generally provides a higher material removal rate than is possible with mere mechanical polishing. This combined chemical and mechanical polishing, commonly referred to as "CMP", is considered an improvement over mere mechanical polishing processes for planarizing or polishing substrates. The CMP technique is common for the manufacture of semiconductor wafers used for the fabrication of integrated circuit die.
Chemical-mechanical polishing (CMP) is performed in the processing of semiconductor wafers and/or chips on commercially available polishers, such as the Westech 372/372M polishers. The standard CMP tools have a circular polishing table and a rotating carrier for holding the substrate.
Difficulties exist ensuring uniformity of polishing of a substrate, such as a silicon wafer using CMP processes. For example, in FIG. 1, a portion of CMP tool 100 is illustrated. CMP tool 100 includes a wafer carrier 102, which provides a vacuum and back pressure through plenum area 104 and holes 106. A vacuum is employed to cause surface 108 of substrate 110 to adhere to wafer carrier 102. CMP tool 100 also includes a primary polish pad 112, which is coupled to primary platen 114. Both wafer carrier 102 and primary platen 114 rotate during CMP processes to polish surface 116 of substrate 110. During rotation, rebound, and other dynamics involving primary polish pad 112 results in deformities of primary polish pad 112, as shown in section 118 of primary polish pad 112. These deformities, resulting from factors, such as pad rebound, result in lower polish rates near edge 120 of substrate 110. Higher polish rates occur just inside edge 120 of substrate 110. In particular, valley 122 and valley 124 result in less polishing occurring in section 126 and section 128 of polish surface 116. Therefore, it would be advantageous to have an improved method and apparatus for CMP that provides for more uniformity of the substrate surface from polishing of the substrate.